Thermally Conductive Silicone Rubber Composition

ABSTRACT

A thermally conductive silicone rubber composition comprising: (A) an organopolysiloxane with the except of below-given components (C) and (E); (B) a thermally conductive filler; (C) a specific organopolysiloxane; (D) a curing agent; and (E) an organopolysiloxane composed of the following units: SiO 4/2 , R 1 R 2   2 SiO 1/2 , and R 2   3 SiO 1/2  (wherein R 1  is a univalent hydrocarbon group with an aliphatic, unsaturated bonds, R 2  may designate the same or different univalent hydrocarbon groups that do not have aliphatic, unsaturated bonds.), said component (E) being used in an amount of 2 to 10 mass % per sum of components (A) and (E), demonstrates high flowability and good handling characteristics in spite of having a large content of thermally conductive filler and that demonstrates good adhesive properties and elongation and tensile strength in spite of the absence of reinforcing filler.

TECHNICAL FIELD

The present invention relates to a thermally conductive silicone rubbercomposition, in particular to a thermally conductive silicone rubbercomposition that demonstrates good handleability and flowability inspite of having a large content of thermally conductive filler and thatdemonstrates good adhesive properties and elongation and tensilestrength in spite of the absence of reinforcing filler.

BACKGROUND ART

An increase in density and in the degree of integration of electronicelements such as transistors, integrated circuits, memory elements, orthe like recently observed in the design of printed circuit boards andhybrid ICs are accompanied by the use of thermally conductive siliconerubber compositions that are characterized by more efficient heatradiation properties.

Such thermally conductive silicone rubber compositions may beexemplified by the following: a thermally conductive silicone rubbercomposition comprising an organopolysiloxane with vinyl groups, anorganohydrogenpolysiloxane, a thermally conductive filler, aminosilane,an adhesion-imparting agent selected from epoxy silane or alkyltitanate,and a platinum-type catalyst (see Japanese Unexamined Patent ApplicationPublication No. (hereinafter referred to as “Kokai”) S61-157569); athermally conductive silicone rubber composition comprising adiorganopolysiloxane that contains in one molecule an average of twoalkenyl groups, an organopolysiloxane that has in one molecule anaverage of three or more silicon-bonded hydrogen atoms, a thermallyconductive filler composed of zinc oxide and magnesium oxide, asurface-treating agent for a filler, and a platinum-type catalyst (seeKokai S62-184058); a thermally conductive silicone rubber compositioncomprising an organopolysiloxane that contains in one molecule at least0.1 mole % of alkenyl groups, an organohydrogenpolysiloxane thatcontains in one molecule at least two silicon-bonded hydrogen atoms, aspherical alumina powder with an average particle size in the range of10 to 50 μm and a spherical or aspherical alumina powder with an averageparticle size below 10 μm, and platinum or a platinum-type compound (seeKokai S63-251466); a thermally conductive silicone rubber compositioncomprising an organopolysiloxane with alkenyl groups, anorganohydrogenpolysiloxane, an amorphous alumina powder with an averageparticle size in the range of 0.1 to 5 μm and a spherical alumina powderwith an average particle size in the range of 5 to 50 μm, and aplatinum-type catalyst (see Kokai H2-41362); and a thermally conductivesilicone rubber composition comprising an organopolysiloxane having inone molecule at least, two alkenyl groups, an organohydrogenpolysiloxanehaving in one molecule at least three silicon-bonded hydrogen atoms, athermally conductive filler with an average particle size in the rangeof 5 to 20 μm, an adhesion-assisting agent, and a platinum orplatinum-type catalyst (see Kokai H2-97559).

However, in order to improve thermal conductivity in a cured bodyobtained from such thermally conductive silicone rubber compositions,the latter must incorporate a large amount of a thermally conductivefiller, but an increase in the amount of such a filler impairshandleability and moldability of the composition, and also worsensphysical properties in products molded from such compositions. Anotherdrawback is low adhesion of the composition to various substrates duringcuring.

In view of the above, it was proposed to improve handleability andmoldability of a thermally conductive silicone rubber composition (1) bypreparing this composition from an organopolysiloxane that contains inone molecule at least two alkenyl groups, an organohydrogenpolysiloxanethat contains in one molecule at least two silicon-bonded hydrogenatoms, an organopolysiloxane that contains in one molecule at least onesilicon-bonded alkoxy group or silicon-bonded hydroxyl group, a finespherical or aspherical alumina powder with an average particle sizebelow 10 μm and a fine spherical or aspherical alumina powder with anaverage particle size in the range of 10 to 50 μm, and a hydrosilylationcatalyst (see Kokai H8-325457); (2) by preparing the composition from anorganopolysiloxane, a methylpolysiloxane that contains a hydrolyzablegroup, a thermally conductive filler, and a curing agent (see Kokai2000-256558); or (3) by preparing the composition from anorganopolysiloxane, a curing agent, and a thermally conductive fillersurface-treated with an oligosiloxane having silicon-bonded alkoxygroups (see Kokai 2001-139815).

However, when the thermally conductive compositions that are mentionedabove incorporate a large amount of a thermally conductive filler suchas alumina for improving thermal conductivity in a silicone rubberobtained by curing the composition, they become extremely viscous andare therefore difficult to handle and to mold. Other problems associatedwith the aforementioned compositions are a decrease in adhesiveproperties, elongation characteristics, and tensile strength of thesilicone rubber obtained by curing the composition. On the other hand,in order to improve the adhesive properties, elongation characteristics,and tensile strength of silicone rubber, the latter should be combinedwith a reinforcing filler, but an addition of the reinforcing filleradversely affects thermal conductivity of the silicone rubber.

It is an object of the present invention to provide a thermallyconductive silicone rubber composition that demonstrates goodhandleability and flowability even when it contains a large amount ofthermally conductive filler added to the composition for obtaining highthermal conductivity, and that is suitable for obtaining thermallyconductive silicone rubber characterized by high tensile strength andimproved adhesion and elongation characteristics even without the use ofa reinforcing filler.

DISCLOSURE OF INVENTION

The thermally conductive silicone rubber composition of the presentinvention comprises:

(A) an organopolysiloxane with the exception of below-given components(C) and (E);(B) a thermally conductive filler;(C) a composition selected from

-   -   (i) an organopolysiloxane represented by the following general        formula:

[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d)

(wherein R¹ is a univalent hydrocarbon group with an aliphatic,unsaturated bonds, R² may designate the same or different univalenthydrocarbon groups that do not have aliphatic, unsaturated bonds, R³designates an alkyl group, alkoxyalkyl group, alkenyl group, or an acylgroup; “a” is an integer between 0 and 3, “b” is 1 or 2, “c” is aninteger between 1 and 3, “d” is an integer between 1 and 3; “(c+d)” isan integer between 2 and 4, “m” is an integer that is equal to orgreater than 0, and “n” is an integer that is equal to or greater than0; when “a” is 0, then “m” is an integer that is equal to or greaterthan 1);

-   -   -   (ii) an organopolysiloxane represented by the following            general formula:

R⁴ ₃SiO(R⁴ ₂SiO)_(p)R⁴ ₂Si—R⁵—SiR⁴ _((3−d))(OR³)_(d)

-   -   -   -   (wherein R³ is the same defined above, R⁴ represents the                same or different univalent hydrocarbon groups, R⁵                represents an oxygen atom or a bivalent hydrocarbon                group, “p” is an integer between 100 and 500, and “d” is                the same defined above); or

        -   (iii) a mixture of two or more of the above constituents (i)            and (ii);            (D) a curing agent; and            (E) an organopolysiloxane composed of the following units:            SiO_(4/2), R¹R² ₂SiO_(1/2), and R² ₃SiO_(1/2) (wherein R¹            and R² are the same as defined above), with the proviso that            component (E) is used in an amount of 2 to 10 mass % per sum            of components (A) and (E).

EFFECTS OF INVENTION

The effects of the invention consist of the fact that the proposedcomposition provides good handleability and flowability even when itcontains a large amount of thermally conductive filler added to thecomposition for obtaining high thermal conductivity, and that it issuitable for obtaining thermally conductive silicone rubbercharacterized by high tensile strength and improved adhesion andelongation characteristics even without the use of a reinforcing filler.

DETAILED DESCRIPTION OF THE INVENTION

The composition of the invention is characterized by comprisingComponents (A) through (E). There are no special restrictions withregard to the curing mechanism of the composition, and the compositioncan be cured by means of a hydrosilylation reaction, condensationreaction, or free-radical reaction with the use of organic peroxide. Themost preferable is a hydrosilylation reaction since it provides quickcuring and does not generate byproducts.

Component (A) is one of the main components of the composition, and itmay be comprised of an organopolysiloxane other than those relating tothe below-described Components (C) and (E). Examples of silicon-bondedgroups contained in Component (A) are the following: methyl, ethyl,propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl,dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,octadecyl, nonadecyl, eicosyl, or similar linear-chain alkyl groups;isopropyl, tertiarybutyl, isobutyl, 2-methylundecyl, 1-hexylheptyl, orsimilar branched-chain alkyl groups; cyclopentyl, cyclohexyl,cyclododecyl, or similar cyclic alkyl groups; vinyl, allyl, butenyl,pentenyl, hexenyl, or similar alkenyl groups; phenyl, tolyl, xylyl, orsimilar aryl groups; benzyl, phenethyl,2-(2,4,6,-trimethylphenyl)propyl, or similar aralkyl groups;3,3,3-trifluoropropyl, 3-chloropropyl, or similar halogenated alkylgroups; silicon-bonded hydrolyzable groups; hydroxyl groups (silanolgroups). Most preferable of the above are alkyl, alkenyl, and arylgroups, especially methyl, vinyl, and phenyl groups. There are nospecial restrictions with regard to the viscosity of Component (A) at25° C., but it is recommended that the viscosity be within the range of20 to 100,000 mPa·s, preferably within the range of 50 to 100,000 mPa·s,more preferably within the range of 50 to 50,000 mPa·s, and mostpreferably within the range of 100 to 50,000 mPa·s. If the viscosity at25° C. is below the recommended lower limit, this will noticeably impairphysical properties of the obtained silicone rubber. If, on the otherhand, the viscosity exceeds the recommended upper limit, this willworsen handleability of the silicone rubber composition. There are nospecial restrictions with regard to the molecular structure of Component(A), and this component may have a linear, branched, partially branchedlinear or dendritic (dendrimer) molecular structure. Component (A) withthe aforementioned molecular structure may be in the form of a simplepolymer, a copolymer, or a mixture of polymers. Most preferable is anorganopolysiloxane with a linear or partially branched linear molecularstructure that does not contain silicon-bonded alkoxy groups.

Component (A) can be exemplified by the following compounds:dimethylpolysiloxane capped at both molecular terminals withdimethylvinylsiloxy groups, dimethylpolysiloxane capped at bothmolecular terminals with methylphenylvinylsiloxy groups, a copolymer ofmethylphenylsiloxane and dimethylsiloxane capped at both molecularterminals with dimethylvinylsiloxy groups; a copolymer ofmethylvinylsiloxane and dimethylsiloxane capped at both molecularterminals with dimethylvinylsiloxy groups, a copolymer ofmethylvinylsiloxane and dimethylsiloxane capped at both molecularterminals with trimethylsiloxy groups, methyl (3,3,3-trifluoropropyl)polysiloxane capped at both molecular terminals with dimethylvinylsiloxygroups; a copolymer of methylvinylsiloxane and dimethylsiloxane cappedat both molecular terminals with silanol groups; a copolymer ofmethylphenylsiloxane, methylvinylsiloxane, and dimethylsiloxane cappedat both molecular terminals with silanol groups; an organosiloxanecopolymer composed of siloxane units represented by the followingsiloxane unit formulas: (CH₃)₃SiO_(1/2), (CH₂)₂(CH₂═CH)SiO_(1/2),CH₃SiO_(3/2) and (CH₂)₂SiO_(2/2); dimethylpolysiloxane capped at bothmolecular terminals with silanol groups; a copolymer ofmethylphenylsiloxane and dimethylsiloxane capped at both molecularterminals with silanol groups; dimethylpolysiloxane capped at bothmolecular terminals with trimethoxysiloxy groups; a copolymer ofmethylphenylsiloxane and dimethylsiloxane capped at both molecularterminals with trimethoxysiloxy groups; dimethylpolysiloxane capped atboth molecular terminals with methyldimethoxysiloxy groups;dimethylpolysiloxane capped at both molecular terminals withtriethoxysiloxy groups; dimethylpolysiloxane capped at both molecularterminals with trimethoxysilylethyl groups; or mixtures of two or moreof the above.

When the composition of the invention is cured by a hydrosilylationreaction, it is recommended that Component (A) be comprised of anorganopolysiloxane with an average of 0.1 or more alkenyl groups in onemolecule, preferably an organopolysiloxane that contains in one moleculeon average more than 0.5 alkenyl groups, and even more preferably anorganopolysiloxane that contains in one molecule on average more than0.8 alkenyl groups. If the average amount of alkenyl groups in onemolecule is below the recommended lower limit, it will be impossible toprovide complete curing of the obtained silicone rubber composition. Thealkenyl groups that are contained in such organopolysiloxanes are thesame as exemplified above, of which vinyl groups are most preferable.Silicon-bonded groups other than alkenyl groups that may be contained inthe aforementioned organopolysiloxanes may be the same linear-chainalkyl groups, branched-chain alkyl groups, cyclic alkyl groups, arylgroups, aralkyl groups, and halogenated alkyl groups that have beenmentioned above. Most preferable of these are alkyl groups, aryl groups,and especially methyl and phenyl groups. There are no specialrestrictions with regard to the viscosity of the aforementionedorganopolysiloxanes at 25° C., but it may be recommended that theviscosity be within the range of 20 to 100,000 mPa·s, preferably withinthe range of 50 to 100,000 mPa·s, more preferably within the range of 50to 50,000 mPa·s, and most preferably within the range of 100 to 50,000mPa·s. If the viscosity is below the recommended lower limit, this willimpair physical properties of the obtained silicone rubber, and if theviscosity exceeds the recommended upper limit, this will noticeablyimpair handleability of the obtained silicone rubber composition. Thereare no limitations with regard to the molecular structure of theaforementioned organopolysiloxanes, but preferably it should have alinear or a partially branched linear molecular structure. Theaforementioned organopolysiloxanes may be exemplified by the sameorganopolysiloxanes with alkenyl groups that have been mentionedearlier.

When the composition of the present invention is curable by acondensation reaction, it is recommended to use as Component (A) anorganopolysiloxane that contains in one molecule at least two silanolgroups or a silicon-bonded hydrolyzable group. The silicon-bondedhydrolyzable groups of such organopolysiloxane may be represented, e.g.,by methoxy, ethoxy, propoxy, or similar alkoxy groups; vinyloxy,propenoxy, isopropenoxy, 1-ethyl-2-methylvinyloxy, or similar alkenoxygroups; methoxyethoxy, ethoxyethoxy, methoxypropoxy, or similaralkoxyalkoxy groups; acetoxy, octanoyloxy, or similar acyloxy groups;dimethylketoxime, methylethylketoxime or similar ketoxime groups;dimethylamino, diethylamino, butylamino, or similar amino groups;dimethylaminoxy, diethylaminoxy, or similar aminoxy groups;N-methylacetoamide, N-ethylacetoamide, or similar amide groups.Silicon-bonded groups other than the silanol and silicon-bondedhydrolyzable groups of the aforementioned organopolysiloxanes may beexemplified by the same linear-chained alkyl groups, branch-chainedalkyl groups, cyclic alkyl groups, alkenyl groups, aryl groups, aralkylgroups, and halogenated alkyl groups that have been mentioned earlier.There are no special restrictions with regard to the viscosity of theaforementioned organopolysiloxanes at 25° C., but it may be recommendedthat the viscosity be within the range of 20 to 100,000 mPa·s,preferably within the range of 50 to 100,000 mPa·s, and most preferablywithin the range of 100 to 100,000 mPa·s. If the viscosity is below therecommended lower limit, this will impair physical properties of theobtained silicone rubber, and if the viscosity exceeds the recommendedupper limit, this will noticeably impair handleability of the obtainedsilicone rubber composition. There are no limitations with regard to themolecular structure of the aforementioned organopolysiloxanes, butpreferably it should have a linear or a partially branched linearmolecular structure. The aforementioned organopolysiloxanes may be thesame organopolysiloxanes with at least two silanol groups or asilicon-bonded hydrolyzable group in one molecule as exemplifiedearlier.

There are no special restrictions with regard to the organopolysiloxanethat can be used as Component (A) in the composition of the presentinvention that is curable by a free-radical reaction with the use of anorganic peroxide, but the preferable one is an organopolysiloxane thatcontains at least one alkenyl group in one molecule. The silicon-bondedgroups contained in such organopolysiloxanes may be the samelinear-chain alkyl groups, branched-chain alkyl groups, cyclic alkylgroups, alkenyl groups, aryl groups, aralkyl groups, and halogenatedalkyl groups that have been mentioned earlier. Most preferable of theseare alkyl groups, alkenyl groups, and aryl groups, especially methyl,vinyl, and phenyl groups. There are no special restrictions with regardto the viscosity of the aforementioned organopolysiloxanes at 25° C.,but it may be recommended that the viscosity be within the range of 20to 100,000 mPa·s, preferably within the range of 50 to 100,000 mPa·s,more preferably within the range of 50 to 50,000 mPa·s, and even morepreferably within the range of 100 to 50,000 mPa·s. If the viscosity isbelow the recommended lower limit, this will impair physical propertiesof the obtained silicone rubber, and if the viscosity exceeds therecommended upper limit, this will noticeably impair handleability ofthe obtained silicone rubber composition. There are no limitations withregard to the molecular structure of the aforementionedorganopolysiloxanes, and they may have the same molecular structures asmentioned earlier, preferably a linear and a partially branched linearmolecular structures. The aforementioned organopolysiloxanes may be thesame organopolysiloxanes that have been exemplified earlier.

Component (B) is a thermally conductive filler that is used to impartthermal conductivity to silicone rubber obtained by curing thecomposition of the invention. Examples of this thermoconductive fillerare the following: aluminum powder, copper powder, nickel powder, or asimilar metal powder; alumina powder, magnesium oxide powder, berylliumoxide powder, chromium oxide powder, titanium oxide powder, or a similarmetal oxide powder; boron nitride powder, aluminum nitride powder, or asimilar metal nitride powder; boron carbide powder, titanium carbidepowder, silicon carbide powder, or a similar metal carbide powder; ametal oxide powder surface-coated with metal for acquiring electricalconductivity; or mixtures of two or more of the powders mentioned above.Furthermore, regarding the shape of the powder particles, Component (B)powders may have spherical, needle-shaped, disc-shaped, cylinder-shaped,or irregular-shaped particles. When it is required that the compositionof the invention or the silicone rubber obtained by curing thecomposition possesses electric insulating properties, then it ispreferable to use Component (B) in the form of metal oxide powders,metal nitride powders, or metal carbide powders, and preferably aluminapowders. There are no special restrictions with regard to the averageparticle size of Component (B), but it may be recommended that theparticle size be within the range of 0.1 to 100 μm, and preferablywithin the range of 0.1 to 50 μm. The most preferable is an aluminapowder with BET-specific surface area not exceeding 5.0 m²/g. When thethermally conductive filler of Component (B) is an alumina powder, itmay be comprised of a mixture of spherical alumina powder (B₁) with anaverage particle size in the range of 1 to 30 μm (excluding 1 μmparticles) and spherical alumina powder or irregular-shaped aluminapowder (B₂) with an average particle size in the range of 0.1 to 5 μm.In such a mixture, it is preferable that the content of constituents(B₁) be within the range of 30 to 90 mass % and the content ofconstituent (B₂) within the range of 10 to 70 mass %.

There are no special limitations with regard to the amount in whichComponent (B) can be added to the composition of the invention. Forexample, in order to mold silicone rubber with improved thermalconductivity, in terms of vol. %, the composition may contain Component(B) in an amount of at least 30 vol. %, preferably 30 to 90 vol. %, morepreferably 40 to 90 vol. %, and even more preferably 50 to 90 vol. %. Inparticular, in the most preferable proportions required for obtainingsilicone rubber with improved thermal conductivity, the amount ofComponent (B) in terms of mass % in the composition of the inventionshould be no less than 60 mass %, preferably within the range of 70 to98 mass %, and more preferably within the range of 80 to 97 mass %. Morespecifically, Component (B) can be added to the composition in an amountof 300 to 2,500 parts by mass, preferably 400 to 2,000 parts by mass,and even more preferably 500 to 2,000 parts by mass per 100 parts bymass of Component (A). If the added amount of Component (B) is below therecommended lower limit, the obtained silicone rubber will not acquiresufficient thermal conductivity. If, on the other hand, the added amountof Component (B) exceeds the recommended upper limit, the viscosity ofthe obtained silicone rubber composition will be too high, and thereforeit will be difficult to provide uniform dispersion of Component (B) inthe obtained silicone rubber composition. This will either impedehandling of the composition or will impair the physical properties inthe silicone rubber obtained from the composition.

Component (C) is used for obtaining a thermally conductive siliconecomposition that possesses high thermal conductivity and goodhandleability even if it contains a large amount of thermoconductivefiller of Component (B). This component may be selected from;

(i) an organopolysiloxane represented by the following general formula:

[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d)

(wherein R¹ is a univalent hydrocarbon group having an aliphatic,unsaturated bond, R² may designate the same or different univalenthydrocarbon groups that do not have aliphatic, unsaturated bonds, R³designates an alkyl group, alkoxyalkyl group, alkenyl group, or an acylgroup; “a” is an integer between 0 and 3, “b” is 1 or 2, “c” is aninteger between 1 and 3, “d” is an integer between 1 and 3; “(c+d)” isan integer between 2 and 4, “m” is an integer that is equal to orgreater than 0, and “n” is an integer that is equal to or greater than0; when “a” is 0, then “m” is an integer that is equal to or greaterthan 1);(ii) an organopolysiloxane represented by the following general formula:

R⁴ ₃SiO(R⁴ ₂SiO)_(p)R⁴ ₂Si—R⁵—SiR⁴ _((3−d))(OR³)_(d)

(wherein R³ is the same defined above, R⁴ represents the same ordifferent univalent hydrocarbon groups, R⁵ represents oxygen atoms orbivalent hydrocarbon groups, “p” is an integer between 100 and 500, and“d” is the same defined above); or(iii) a mixture of two or more of the above constituents (i) and (ii).

Even if the aforementioned constituent (i), which is added for obtainingsilicone rubber of high thermal conductivity, is used in the thermalconductive filler of Component (B) in a large quantity, this will notimpair handleability or moldability of the composition, and when thecomposition possesses curability, this constituent imparts to thecomposition good adhesion to various substrates during curing. Theconstituent (i) is represented by the following general formula:

[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d)

wherein R¹ is a univalent hydrocarbon group that contains aliphatic,unsaturated bonds. Examples of such groups are the following: vinyl,allyl, butenyl, hexenyl, decenyl, undecenyl, dodecenyl, tridecenyl,tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl,nonadecenyl, eicosenyl, or similar linear-chain alkenyl groups;isopropenyl, 2-methyl-2-propenyl, 2-methyl-10-undecenyl, or similarbranched-chain alkenyl groups; vinylcyclohexyl, vinylcyclododecyl, orsimilar cyclic alkyl groups that contain aliphatic, unsaturated bonds;vinylphenyl or similar aryl groups that contain aliphatic, unsaturatedbonds; vinylbenzyl, vinylphenethyl, or similar aralkyl groups thatcontain aliphatic, unsaturated bonds. Most preferable of the above arelinear-chain alkenyl groups, in particular, vinyl, allyl, or hexenylgroups. There are no special restrictions with regard to the position ofthe aliphatic, unsaturated bonds in R¹, but it is preferable to locatethem remotely from the bonding silicon atom. In the above formula, R²may represent similar or different univalent hydrocarbon groups that donot contain aliphatic, unsaturated bonds. These groups may be the samelinear-chain alkyl groups, branched-chain alkyl groups, cyclic alkylgroups, aryl groups, aralkyl groups, or halogenated alkyl groups thathave been exemplified above. Most preferable of these groups are alkyland aryl groups, and even more preferable are alkyl groups having one tofour carbon atoms, in particular, methyl and ethyl groups. In the aboveformula, R³ is an alkyl group, alkoxyalkyl group, alkenyl group, or acylgroup. R³ as an alkyl group can be represented by the same linear-chainalkyl groups, branched-chain alkyl groups, or cyclic alkyl groups thathave been given above. Linear-chain alkyl groups are more preferable,especially groups such as methyl, ethyl, or propyl groups. R³ as analkoxyalkyl group may be exemplified by methoxyethoxy, ethoxyethoxy, ormethoxypropoxy groups, of which methoxyethoxy groups are mostpreferable. R³ as alkenyl groups may be the same alkenyl groups thathave been exemplified above, and preferably be comprised of isopropenylgroups. R³ as acyl groups may be comprised, e.g., of acetoxy groups. Inthe above formula, “a” is an integer between 0 and 3, and preferably 1;“b” is 1 or 2, and preferably 1; “c” is an integer between 1 and 3, andpreferable 1; “d” is an integer between 1 and 3, and preferably 3; and“(c+d)” is an integer between 2 and 4; “m” is an integer equal to orgreater than 0. When the aforementioned “a” is 0, then “m” in the aboveformula is an integer equal to or greater than 1. It is preferable that“m” be an integer between 0 and 500, preferably between 1 and 500, morepreferably between 5 and 500, and even more preferably between 10 and500, and most preferably between 10 and 200. In the above formula, “n”is an integer equal to or greater than 0, preferably between 0 and 500,even more preferably between 1 and 500, still further preferably between5 and 500, even more preferably between 10 and 500, and most preferablybetween 10 and 200.

The aforementioned organopolysiloxane of constituent (i) can beprepared, e.g., by conducting an alkoxy-exchange reaction between anorganosiloxane which is represented by the following formula:

[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]H

and is capped at one molecular terminal with silanol groups and analkoxysilane compound that contains in one molecule at least twosilicon-bonded alkoxy groups, the reaction being carried out in thepresence of acetic acid or a similar acidic catalyst. In the aboveformula of the aforementioned silanol-capped organosiloxane, R¹ and R²are the same groups as defined above; “a”, “b”, “m”, and “n” are alsothe same integers as defined earlier. On the other hand, theaforementioned alkoxysilane compound that contains in one molecule atleast two silicon-bonded alkoxy groups is represented by the followinggeneral formula:

R² _((4−f))Si(OR³)_(f).

In the formula of the alkoxysilane compound, R² and R³ are the same asdefined earlier, and “f” is an integer between 2 and 4, preferably 4.The aforementioned alkoxysilane compound can be exemplified bydimethoxydimethylsilane, dimethoxydiethylsilane, diethoxydimethylsilane,diethoxydiethylsilane, or a similar dialkoxydialkylsilane compound;trimethoxymethylsilane, trimethoxyethylsilane, trimethoxypropylsilane,triethoxymethylsilane, triethoxyethylsilane, or a similartrialkoxyalkylsilane compound; tetramethoxysilane, tetraethyoxysilane,tetrapropoxysilane, or a similar tetraalkoxysilane compound. The acidiccatalyst may be represented by, e.g., acetic acid, propionic acid, or asimilar fatty acid.

The organopolysiloxanes of constituent (i) may be exemplified bycompounds represented by the following formulas:

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₅Si(OCH₃)₃

(CH₂═CHCH₂)(CH₃)₂SiO[(CH₃)₂SiO]₅Si(OCH₃)₃

(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₃)₂SiO]₅Si(OCH₃)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₇Si(OCH₃)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₇Si(OC₂H₅)₃

(CH₂═CHCH₂)(CH₃)₂SiO[(CH₃)₂SiO]₇Si(OCH₃)₃

(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₃)₂SiO]₇Si(OCH₃)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₇SiCH₃(OCH₃)₂

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₇SiCH₃(OCH₃)₂

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₂₅Si(OCH₃)₃

(CH₂═CHCH₂)(CH₃)₂SiO[(CH₃)₂SiO]₂₅Si(OCH₃)₃

(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₃)₂SiO]₂₅Si(OCH₃)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₂₅Si(OC₂H₅)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₂₅SiCH₃(OCH₃)₂

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₅₀Si(OCH₃)₃

(CH₂═CHCH₂)(CH₃)₂SiO[(CH₃)₂SiO]₅₀Si(OCH₃)₃

(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₃)₂SiO]₅₀Si(OCH₃)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₅₀Si(OC₂H₅)₃

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₅₀SiCH₃(OCH₃)₂

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)₂SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OC₂H₅)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)₂SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OC₂H₅)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)₂SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CHCH₂)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₁[(CH₃)₂SiO]₄}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)₂SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OC₂H₅)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)₂SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OC₂H₅)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)₂SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CHCH₂)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₂[(CH₃)₂SiO]₁₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)₂SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OC₂H₅)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)₂SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OC₂H₅)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)₂SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CHCH₂)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₃[(CH₃)₂SiO]₂₂}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)₂SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OC₂H₅)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)₂SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CH)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OC₂H₅)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂)₂SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CHCH₂)(CH₃)₂SiO[(CH₂═CHCH₂)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₃)₃SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CH)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

{(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)₂SiO[(CH₂═CHCH₂CH₂CH₂CH₂)(CH₃)SiO]₄[(CH₃)₂SiO]₅₀}Si(OCH₃)₃

The organosiloxane of constituent (ii) is a constituent that allows theobtaining of a thermally conductive silicone rubber composition that hasgood handleability even when a thermally conductive filler of Component(B) is used in a large amount for producing thermally conductivesilicone rubber. This constituent is expressed by the following generalformula:

R⁴ ₃SiO(R⁴ ₂SiO)_(p)R⁴ ₂Si—R⁵—SiR⁴ _((3−d))(OR³)_(d).

In this formula, R⁴ may represent the same or different univalenthydrocarbon groups, which may be represented by the same linear-chainalkyl groups, branched-chain alkyl groups, cyclic alkyl groups, arylgroups, aralkyl groups, alkenyl groups, or halogenated alkyl groups, asmentioned above. The most preferable of these are linear-chain alkylgroups, especially methyl groups. Furthermore, in the above formula, R⁵represents an oxygen atom or a bivalent hydrocarbon group. The bivalenthydrocarbon groups of R⁵ may be exemplified by methylene, ethylene,propylene, isopropylene, butylene, or similar alkylene groups;ethyleneoxyethylene, ethyleneoxypropylene, or similaralkyleneoxyalkylene groups. The most preferable R⁵ is an oxygen atom. Inthe above formula, R³ is the same as defined above. “p” is an integerbetween 100 and 500, preferably between 105 and 500, more preferablybetween 110 and 500, and most preferably between 110 and 200. If thevalue of “p” is below the recommended lower limit, it may be impossibleto use Component (B) in large quantities in the preparation of thermallyconductive rubber. On the other hand, if the value of “p” exceeds therecommended upper limit, this will cause an excessive increase in thevolume of molecules bound to the surface, and it will be an obstacle forusing Component (B) in a large quantity. This tendency is revealed whenthe content of Component (B) in the composition of the invention isextremely high and exceeds 80 vol. % because this shortens the distancesbetween particles in Component (B). In the above formula, “d” is aninteger between 1 and 3, preferably 3.

The organosiloxane of constituent (ii) can be represented by compoundsof the following formulas:

(CH₃)₃SiO[(CH₃)₂SiO]₁₁₈(CH₃)₂Si—O—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₁₂₅(CH₃)₂Si—O—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₁₄₀(CH₃)₂Si—O—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₁₆₀(CH₃)₂Si —O—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₂₀₀(CH₃)₂Si —O—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₃₀₀(CH₃)₂Si—C₂H₄—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₁₁₈(CH₃)₂Si —O—SiCH₃(OCH₃)₂

(CH₃)₃SiO[(CH₃)₂SiO]₇₉[(CH₃)(C₆H₅)SiO]₃₀—Si(OCH₃)₃

(CH₃)₃SiO[(CH₃)₂SiO]₇₉[(C₆H₅)₂SiO]₃₀—Si(OCH₃)₃

There are no special restrictions with regard to the amounts in whichComponent (C) can be used in the composition, and its dispersity in theprepared thermally conductive silicone rubber composition can beimproved when it treats the surface of Composition (B). Morespecifically, Component (C) can be used in an amount within the range of0.1 to 10 parts by mass, preferably 0.1 to 5 parts by mass per 100 partsby mass of Component (B). If Component (C) is used in an amount lessthan the recommended lower limit, then, in combination with a largequantity of Component (B), this will either impair the physicalproperties and moldability of the obtained silicone rubber compositionor will cause precipitation and separation of Component (B) from theobtained silicone rubber composition during storage. If, on the otherhand, the amount of Component (C) exceeds the recommended upper limit,it will adversely affect the physical characteristics of the obtainedsilicone rubber. Two or more types of Component (C) can be usedsimultaneously. Component (C) may also be used in combination with thealkoxysilane compound of the aforementioned formula:

R² _((4−f))Si(OR³)_(f),

wherein R² and R³ are the same groups as defined above, and “f” is aninteger between 1 and 4.

Component (C) can be added to the composition by using the followingmethods: (1) Component (C) is mixed with Component (B), and thenComponent (B) surface-treated with Component (C) is added; (2) Component(C) is added to a mixture of Components (A) and (B), and then Component(B) surface-treated with Component (C) in Component (A) is added; (3)all Components (A), (B), and (C) are mixed simultaneously, and thenComponent (B) surface-treated with Component (C) is added. Mostpreferable is method (3). Thus, Component (C) may be used in the form ofcoating on the surface of Component (B) or can be added independently.In order to accelerate surface treatment of Component (B) with Component(C), the process may be carried out with heating or by using an acidicsubstance, such as acetic acid, phosphoric acid, etc., in combinationwith a basic substance such as a trialkylamine, tertiary ammonium salts,gaseous ammonia, ammonium carbonate, etc.

When curing of the composition is carried out by means of ahydrosilylation reaction, curing agent (D) is composed of anorganopolysiloxane having on average two or more silicon-bonded hydrogenatoms in one molecule and a platinum catalyst. The silicon-bonded groupsof the aforementioned organopolysiloxane are the same linear-chain alkylgroups, branched-chain alkyl groups, cyclic alkyl groups, aryl groups,aralkyl groups, and halogenated alkyl groups that have been mentionedearlier, of which most preferable are alkyl and aryl groups, especiallymethyl and phenyl groups. There are no special restrictions with regardto the viscosity of this organopolysiloxane at 25° C., preferably theviscosity should be within the range of 1 to 100,000 mPa·s, andpreferably in the range of 1 to 5,000 mPa·s. There are no restrictionsto the molecular structure of the aforementioned organopolysiloxane thatmay have a linear-chain, branched-chain, partially branchedlinear-chain, cyclic, or dendritic (dendrimer) molecular structure. Suchmolecular structures may be contained in polymers, copolymers, andpolymer mixtures of the aforementioned organopolysiloxane.

The organopolysiloxane mentioned above may be represented by thefollowing compounds: dimethylpolysiloxane capped at both molecularterminals with dimethylhydrogensiloxy groups; a copolymer ofmethylhydrogensiloxane and dimethylsiloxane capped at both molecularterminals with trimethylsiloxy groups; a copolymer ofmethylhydrogensiloxane and dimethylsiloxane capped at both molecularterminals with dimethylhydrogensiloxy groups; an organosiloxanecopolymer composed of siloxane units represented by the followingformulas: (CH₃)₃SiO_(1/2), (CH₃)₂ HSiO_(1/2), and SiO_(4/2); or mixturesof two or more of the above.

The last-mentioned organopolysiloxane should be used in amount requiredfor curing the composition. More specifically, it should be added insuch an amount that the content of silicon-bonded hydrogen atoms in thiscomponent constitutes 0.1 to 10 moles, preferably 0.1 to 5 moles, andeven more preferably 0.1 to 3.0 moles per 1 mole of silicon-bondedalkenyl groups in Component (A). If the content of this component isbelow the recommended lower limit, the obtained silicone compositionwill reveal a tendency toward incomplete curing; if, on the other hand,the content exceeds the recommended upper limit, the obtained siliconerubber will be too hard and will show a tendency toward an increase insurface cracking.

The platinum-type catalyst is used in the composition for acceleratingthe process of curing. Examples of such a catalyst are chloroplatinicacid, an alcohol solution of chloroplatinic acid, platinum-olefincomplex, platinum-alkenylsiloxane complex, and platinum-carbonylcomplex.

The platinum-type catalyst should be used in an amount required forcuring the composition of the invention. In particular, in terms of massunits, it should be added in an amount of 0.01 to 1,000 ppm, preferably0.1 to 500 ppm of metallic platinum per Component (A). If the addedamount of the catalyst is below the recommended lower limit, there willbe a tendency toward incomplete curing of the obtained silicone rubbercomposition, and if, on the other hand, it is added in an amountexceeding the recommended upper limit, this will not produce anoticeable effect.

When the composition is cured by a condensation reaction, Component (D)is comprised of a silane that contains in one molecule at least threesilicon-bonded hydrolyzable groups, or its partially hydrolyzed product.If necessary, Component (D) may also be comprised of acondensation-reaction catalyst. The silicon-bonded hydrolyzable groupscontained in the silane may be exemplified by the same alkoxy,alkoxyalkoxy, acyloxy, ketoxime, alkenoxy, amino, aminoxy, and amidegroups as those mentioned above. Groups other than the aforementionedhydrolyzable groups on silicone atoms of the silane may be exemplifiedby the same linear-chain alkyl groups, branched-chain alkyl groups,cyclic alkyl groups, alkenyl groups, aryl groups, aralkyl groups, andhalogenated alkyl groups as those mentioned above. Most preferablesilanes or their hydrolyzed products can be exemplified bymethyltriethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, andethylorthosilicate.

The aforementioned silane or hydrolyzed product thereof should be usedin the composition in an amount required for curing of the composition,in particular, in an amount of 0.01 to 20 parts by mass, preferably 0.1to 10 parts by mass per 100 parts by mass of Component (A). If thesilane or the hydrolyzed product thereof is used in an amount below therecommended lower limit, this will impair the storage stability of theobtained composition and will lower the adhesive strength of thecomposition. If they are used in an amount exceeding the recommendedupper limit, this will noticeably delay the curing process.

The condensation-reaction catalysts may also comprise arbitrarycomponents which are not indispensable when a curing agent that containsa silane with aminoxy, amine, ketoxime, or similar hydrolyzable groupsis used. Examples of such condensation-reaction catalysts are thefollowing: tetrabutyl titanate, tetraisopropyl titanate, or similarorgano titanic acid esters; diisopropoxy bis(acetylacetate) titanium,diisopropoxy bis(ethylacetoacetate) titanium, or similar organo titaniumchelate compounds; aluminum tris(acetylacetonate), aluminumtris(ethylacetoacetate), or similar organo aluminum compounds; zirconiumtetra(acetylacetonate), zirconium tetrabutylate, or similar organiczirconium compounds; dibutyl tin dioctoate, dibutyl tin dilaurate, butyltin-2-ethylhexoate, or similar organic tin compounds; tin naphthenate,tin oleate, tin butylate, cobalt naphthenate, zinc stearate, or similarmetal salts of organic carboxylic acids; hexylamine, dodecylaminephosphate, or similar amine compounds or their salts; benzyltriethylammonium acetate, or similar tertiary ammonium salts; potassium acetate,lithium nitrate, or similar lower fatty acid salts of alkali metals;dimethylhydroxylamine, diethylhydroxylamine, or similardialkylhydroxylamines; and organic silicon compounds that containguanidyl groups.

The aforementioned condensation-reaction catalyst can be used in thecomposition in arbitrary amounts, provided that these amounts ensurecuring. In particular, this catalyst can be used in an amount of 0.01 to20 parts by mass, preferably 0.1 to 10 parts by mass per 100 parts bymass of Component (A). When the aforementioned catalyst is anindispensable component and is used in an amount less than the lowerlimit recommended above, it would be difficult to provide completecuring of the composition. If, on the other hand, the amount of thecatalyst exceeds the recommended upper limit, this will impair storagestability of the composition.

When curing is carried out by a free-radical reaction with the use of anorganic peroxide compound, then Component (D) should be comprised of anorganic peroxide compound such as benzoyl peroxide, dicumyl peroxide,2,5-dimethyl bis(2,5-t-butylperoxy) hexane, di-t-butylperoxide, andt-butylperbenzoate. The organic peroxides should be used in amountssufficient for curing, in particular, in an amount of 0.1 to 5 parts bymass per 100 parts by mass of the organopolysiloxane that constitutesComponent (A).

Component (E) is an organopolysiloxane that significantly improves thephysical characteristics of silicone rubber obtained by curing thepresent composition. This component consists of the following units:SiO_(4/2), R¹R² ₂SiO_(1/2), and R² ₃SiO_(1/2). In the above formulas, R¹is a univalent hydrocarbon group that contains unsaturated aliphaticbonds. The aforementioned univalent hydrocarbon group may be exemplifiedby the same groups as mentioned above, in particular, vinyl groups. Inthe above formula, R² designates a univalent hydrocarbon group that doesnot contain unsaturated aliphatic bonds. This group is the same asexemplified above for R², in particular, methyl and phenyl groups. Themost preferable organopolysiloxane of Component (E) composed of theaforementioned units is the one represented by the following formula:

(SiO_(4/2))_(g)(R¹R² ₂SiO_(1/2))_(h)(R² ₃SiO_(1/2))_(i).

Wherein R¹ and R² are the same groups as defined above; “g”, “h”, and“i” are positive numbers; and “(h+i)/g” is within the range of 0.3 to3.0, preferably within the range of 0.3 to 2.5, and most preferablywithin the range of 0.3 to 2.0. It is recommended that “i/g” be withinthe range of 0.01 to 2.0, preferably within the range of 0.02 to 2.0,and most preferably within the range of 0.03 to 2.0. There are nospecial restrictions with regard to the mass-average molecular weight ofthe aforementioned Component (E), but it may be recommended to provide amass-average molecular weight in the range of 1,000 to 20,000,preferably 5,000 to 20,000, and most preferably 10,000 to 20,000.

The organopolysiloxane of Component (E) can be prepared byco-hydrolyzing the silanes of the formulas given below and by subjectingthem to a condensation reaction: SiX₄, R¹R² ₂SiX, and R² ₃SiX, whereinR¹ and R² are the same groups as defined above, X designates a halogenatom such as chlorine, bromine, iodine, etc., or a methoxy group, ethoxygroup, propoxy group, or a similar alkoxy group. When hydrolysis and acondensation reaction are carried out, it is recommended to conduct thereaction in the presence of a trifluoroacetic acid or a similar acid.

Component (E) can be used in the composition in an amount of 2 to 10mass % per sum of Components (A) and (E). If it is used in an amountbelow the recommended lower limit, this will lower the physicalcharacteristics of the obtained silicone rubber and will impair adhesiveproperties. On the other hand, if the added amount exceeds therecommended upper limit, the cured object will lose its rubber-likeproperties and will be too hard and brittle.

Other arbitrary components that can be added to the composition areexemplified by adhesion-imparting agents such as a siloxane compoundthat contains in one molecule at least one alkenyl group andsilicon-bonded alkoxy group; a siloxane compound that contains in onemolecule at least one silicon-bonded hydrogen atom and at least onesilicon-bonded alkoxy group; a siloxane compound that contains in onemolecule at least one alkenyl group, at least one silicon-bonded alkoxygroup, and at least one epoxy-containing organic group; a siloxanecompound that contains in one molecule at least one silicon-bondedhydrogen atom, at least one silicon-bonded alkoxy group, and at leastone epoxy-containing organic group; a siloxane compound that contains inone molecule at least one alkenyl group, at least one silicon-bondedalkoxy group, and at least one organic group that contains a methacrylicgroup; a siloxane compound that contains in one molecule at least onesilicon-bonded hydrogen atom, at least one silicon-bonded alkoxy group,and at least one organic group that contains an acrylic or methacrylicgroup; a mixture or a reaction mixture composed of a siloxane compoundor an alkoxysilane compound that contains an epoxy-containing organicgroup and a siloxane compound that contains in one molecule at least onesilicon-bonded hydroxy group and at least one silicon-bonded alkenylgroup. The aforementioned epoxy-containing organic groups can beexemplified by 3-glicidoxypropyl, 4-glicidoxybutyl, or similarglycidoxyalkyl groups; 2-(3,4-epoxycyclohexyl)-ethyl,3-(3,4-epoxycyclohexyl)-propyl, or similar epoxycyclohexylalkyl groups;4-oxiranylbutyl, 8-oxiranyloctyl, or similar oxiranylalkyl groups. Theaforementioned organic groups that contain acrylic or methacrylic groupsmay be exemplified by 3-methacryloxypropyl, 3-acryloxypropyl, and4-methacryloxybutyl groups. There are no special restrictions withregard to the amounts in which the aforementioned adhesion-impartingagents can be used, but it may be recommended to use them in an amountof 0.001 to 10 mass % of the composition, preferably in an amount of0.01 to 10 mass %, and most preferably 0.1 to 10 mass %.

Examples of other arbitrary components that can be added to thecomposition are the following: methyltrimethoxysilane,methylethyldimethoxysilane, methyltriethoxysilane,ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane,pentyltrimethoxysilane, hexyltrimethoxysilane, heptyltrimethoxysilane,octyltrimethoxysilane, octylmethyl dimethoxysilane,decyltrimethoxysilane, decyltriethoxysilane, or similar alkyl-containingalkoxysilanes that can be contained in the composition assurface-treating agents of the aforementioned Component (B). There areno special restrictions with regard to the amounts in which theaforementioned alkyl-containing alkoxysilanes can be used, but it willbe sufficient if they cover at least 10% of the surface of Component (B)and preferably more than 50%. The amount of an alkyl-containingalkoxysilane that has to be used in the composition can be determined bythe formula given below. Since the minimal surface area coated with analkyl-containing alkoxysilane can be calculated by the molecular modelof Stuart-Briegleb, such a surface can be determined as78.3×1000/(molecular weight of alkyl-containing alkoxysilane).

Therefore, the following expression can be written:

${M = \frac{\begin{bmatrix}\left( {{amount}\mspace{14mu} {of}\mspace{14mu} {Component}\mspace{14mu} (B)(g) \times} \right. \\{{BET}\text{-}{specific}\mspace{14mu} {area}\mspace{14mu} {of}\mspace{14mu} {Component}\mspace{14mu} (B)\left( {m^{2}\text{/}g} \right)}\end{bmatrix}}{\begin{bmatrix}{{minimal}\mspace{14mu} {surface}\mspace{14mu} {area}\mspace{14mu} {coated}} \\{{with}\mspace{14mu} {the}\mspace{14mu} {alkyl}\text{-}{containing}\mspace{14mu} {alkoxysilane}\mspace{14mu} \left( {m^{2}\text{/}g} \right)}\end{bmatrix}}},$

wherein M is the amount of alkyl-containing alkoxysilane (g). Within thelimits that do not interfere with the objects of the present invention,the composition may also be combined with additives such as pigments,dyes, fluorescent dyes, heat-resistant additives, triazole-typecompounds, or other flame-retarding agents, plasticizers, andadhesion-imparting agents. In particular, when curing is carried out bymeans of a hydrosilylation reaction, the speed of curing of thecomposition can be adjusted and handleability can be improved when thecomposition is combined with 2-methyl-3-butyn-2-ol,2-phenyl-3-butyn-2-ol, 1-ethynyl-1-cyclohexanol, or similaracetylene-type compounds; 3-methyl-3-penten-1-yne,3,5-dimethyl-3-hexen-1-yne, or similar enyne compounds; as well ashydrazine-type compounds, phosphine-type compounds, mercaptane-typecompounds, or similar curing inhibitors. There are no specialrestrictions with regard to the amounts in which the aforementionedcuring inhibitors can be used, but it may be recommended to use them inan amount of 0.0001 to 1.0 mass %.

EXAMPLES

The thermally conductive silicone rubber composition of the inventionwill be further described in more detail by means of practical andcomparative examples. The coefficients of thermal conductivity given inthe examples were measured at 50° C. and all other characteristics weremeasured at 25° C.

Furthermore, the following starting materials were used in the practicaland comparative examples.

Constituent (A1): dimethylpolysiloxane capped at both molecularterminals with dimethylvinylsiloxy groups (viscosity=2,000 mPa·s;content of vinyl groups=0.22 mass %);Constituent (A2): dimethylpolysiloxane capped at both molecularterminals with dimethylvinylsiloxy groups (viscosity=10,700 mPa·s;content of vinyl groups=0.137 mass %);Constituent (A3): dimethylpolysiloxane capped at both molecularterminals with dimethylvinylsiloxy groups (viscosity=2,100 mPa·s;content of vinyl groups=0.22 mass %);Constituent (A4): dimethylpolysiloxane capped at both molecularterminals with dimethylvinylsiloxy groups (viscosity=11,500 mPa·s;content of vinyl groups=0.137 mass %);Constituent (B1): spherical alumina powder with BET-specific surfacearea of 0.4 m²/g and with an average particle size of 10 μm;Constituent (B2): irregular-shaped alumina powder with BET-specificsurface area of 2.37 m²/g and with an average particle size of 1.1 μm;Constituent (C1): organopolysiloxane represented by the followingformula:

(CH₂═CH)(CH₃)₂SiO[(CH₃)₂SiO]₂₇Si(OCH₃)₃;

Constituent (C2): organopolysiloxane represented by the followingformula:

(CH₃)₃SiO[(CH₃)₂SiO]₁₁₀Si(OCH₃)₃;

Constituent (D1): complex of platinum and1,3-divinyl-1,1,3,3-tetramethyldisiloxane with 0.5 mass % of metallicplatinum;Constituent (D2): a copolymer of methylhydrogensiloxane anddimethylsiloxane capped at both molecular terminals with trimethylsiloxygroups that contains in one molecule on average five silicon-bondedhydrogen atoms (viscosity=5 mPa·s; content of silicon-bonded hydrogenatoms=0.74 mass %);Constituent (E1): mixture of dimethylpolysiloxane capped at bothmolecular terminals with dimethylvinylsiloxy groups (viscosity=2,000mPa·s; content of vinyl groups=0.22 mass %) and organopolysiloxanerepresented by the following average unit formula:

[(CH₂═CH)(CH₃)₂SiO_(1/2)]_(0.02)[(CH₃)₃SiO_(1/2)]_(0.43)(SiO_(4/2))_(0.55),

with the content of said organopolysiloxane is 28 mass % per themixture;Constituent (F1): a copolymer of dimethylsiloxane andmethylvinylsiloxane capped at both terminals with 3-glycidoxypropyldimethoxysiloxy groups (viscosity=20 mPa·s; content of vinyl groups=9.6mass %);Constituent (G1): a mixture of dimethylpolysiloxane capped at bothmolecular terminals with dimethylvinylsiloxy groups (viscosity=2,000mPa·s; content of vinyl groups=0.22 mass %) and carbon black (ThermaxFloform N-990, the product of Cancarb Co.), with the content of saidcarbon black is 50 mass % per the mixture;

Practical Example 1

Liquid Component (A) was prepared by mixing the following constituentsat room temperature: 5.21 parts by mass of Constituent (A1); 1.48 partsby mass of Constituent (A2); 25.01 parts by mass of Constituent (B1);16.99 parts by mass of Constituent (B2); 0.13 parts by mass ofConstituent (C1); 0.13 parts by mass of Constituent (C2); 1.00 part bymass of Constituent (E1); and 0.05 parts by mass of Constituent (D1).

Independently, liquid Component (B) was prepared by mixing the followingconstituents at room temperature: 4.31 parts by mass of Constituent(A1); 1.23 parts by mass of Constituent (A2); 25.01 parts by mass ofConstituent (B1); 16.99 parts by mass of Constituent (B2); 0.13 parts bymass of Constituent (C1); 0.13 parts by mass of Constituent (C2); 1.00part by mass of Constituent (E1); 0.70 parts by mass of Constituent(D2), and 0.50 parts by mass of Constituent (F1).

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.54; the content of Constituent (B1) and Constituent (B2) was 57 vol.%, and the content of Constituent (E1) was 3.9 mass % per the sum ofConstituents (A1), (A2), and (E1). Characteristics of the obtainedthermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured by the methods described below,and the results of the measurements are shown in Table 1.

[Viscosity of Thermally Conductive Silicone Rubber Composition]

This characteristic was measured by means of the rheometer (AR 550; theproduct of TA Instruments Co., Ltd.). The geometry was a 20 mm diameter.And a 2°-cone/plate was used. The viscosity was measured at differentspeeds of rotation, such as 0.3 rpm and 3.4 rpm. Upon completion ofmeasurements at 0.3 rpm, the sample was left intact for 5 min., and thenthe measurement was continued at 3.4 rpm. The viscosity was the valueobtained in each measurement after 10 min.

[Coefficient of Thermal Conductivity of Silicone Rubber]

In accordance with the conventional method for measuring coefficients ofthermal conductivity in thermally conductive silicone rubbercompositions, the respective coefficient of silicone rubber was measuredby a tester for measuring thermal resistance of resins (the product ofHitachi Seisakusho Co., Ltd.). In the measurement specimens, thethermally conductive silicone rubber composition was sandwiched betweentwo silicon chips of Hitachi Seisakusho Co., Ltd., having areas of 1cm×1 cm and thicknesses of 0.0725 cm, and was squeezed to thicknesses of50 μm, 100 μm, and 150 μm, and then cured by heating for 30 min. at 150°C. Thermal resistance in specimens of different thicknesses was measuredat a load of 50 N and at 50° C. The values of thermal resistance wereused for calculating respective coefficients of thermal conductivity.

[Adhesive Strength of Thermally Conductive Silicone Rubber]

A thermally conductive silicone rubber composition was sandwichedbetween adherends and cured for 30 min. at 150° C. The adherends werecomprised of aluminum plates from Paltec Co. Ltd. (JIS H 4000 A1050P).The area of adhesion was 25 mm×10 mm, and the thickness of the adhesivelayer was equal to 1 mm. Tensile shear adhesive strength of the obtainedthermally conductive rubber was measured according to JIS K 6249.

[Elongation of Thermally Conductive Silicone Rubber]

The obtained thermally conductive silicone rubber composition was pouredinto a mold having an area of 120 mm×120 mm and a depth of 2 mm, and athermally conductive silicone rubber sheet was produced by heating thecomposition for 15 min. at 150° C. The sheet was again heated for 60min. at 150° C., whereby a specimen was produced. The specimen wastested with regard to elongation of the obtained thermally conductivesilicone rubber according to JIS K 6251.

[Tensile Strength of Thermally Conductive Silicone Rubber]

A thermally conductive silicone rubber sheet was produced by the samemethod as described above and turned into a specimen. Tensile strengthof the obtained thermally conductive silicone rubber was measureaccording to JIS K 6251.

[Hardness of Thermally Conductive Silicone Rubber]

A thermally conductive silicone rubber sheet was produced by the samemethod as described above and turned into a specimen. Hardness of theobtained thermally conductive silicone rubber was measured by a type-Adurometer according to JIS K 6253.

Practical Example 2

Liquid Component (A) was prepared by mixing the following constituentsat room temperature: 4.20 parts by mass of Constituent (A1); 1.40 partsby mass of Constituent (A2); 25.01 parts by mass of Constituent (B1);16.99 parts by mass of Constituent (B2); 0.13 parts by mass ofConstituent (C1); 0.13 parts by mass of Constituent (C2); 2.15 parts bymass of Constituent (E1); and 0.05 parts by mass of Constituent (D1).

Independently, liquid Component (B) was prepared by mixing the followingconstituents at room temperature: 3.22 parts by mass of Constituent(A1); 1.07 parts by mass of Constituent (A2); 25.01 parts by mass ofConstituent (B1); 16.99 parts by mass of Constituent (B2); 0.13 parts bymass of Constituent (C1); 0.13 parts by mass of Constituent (C2); 2.15parts by mass of Constituent (E1); 0.80 parts by mass of Constituent(D2), and 0.50 parts by mass of Constituent (F1).

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.54; the content of Constituent (B1) and Constituent (B2) was 57 vol.%, and the content of Constituent (E1) was 8.5 mass % per the sum ofConstituents (A1), (A2), and (E1). Characteristics of the obtainedthermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured by the same methods as inPractical Example 1, and the results of the measurements are shown inTable 1.

Practical Example 3

A mixture was prepared by mixing for 15 min. the following components:16.54 parts by mass of Constituent (A1); 5.68 parts by mass ofConstituent (A2); 100.00 parts by mass of Constituent (B1); 68.00 partsby mass of Constituent (B2); 0.50 parts by mass of Constituent (C1);0.49 parts by mass of Constituent (C2); and 8.60 parts by mass ofConstituent (E1). The obtained mixture was further mixed for 1 hr. at150° C. and under a reduced pressure below 10 mmHg. Following this, thecontents were cooled to room temperature for 30 min. under mixingconditions. The mixture was further combined with 0.22 parts by mass ofconstituent (D1), mixed for 15 min. at room temperature, and then mixedfor another 30 min. under a pressure below 10 mmHg. As a result, liquidComponent (A) was prepared.

Independently, another mixture was prepared by mixing for 15 min. thefollowing constituents: 12.52 parts by mass of Constituent (A1); 4.68parts by mass of Constituent (A2); 100.00 parts by mass of Constituent(B1); 68.00 parts by mass of Constituent (B2); 0.50 parts by mass ofConstituent (C1); 0.50 parts by mass of Constituent (C2); and 8.62 partsby mass of Constituent (E1). The obtained mixture was further mixed for1 hr. at 150° C. and under a reduced pressure below 10 mmHg. Followingthis, the contents were cooled to room temperature for 30 min. undermixing conditions. The obtained mixture was further combined with 3.25parts by mass of Constituent (D2) and 2.00 parts by mass of Constituent(F1). The contents were further mixed at room temperature for 15 min,and then were mixed for 30 min. under a reduced pressure below 10 mmHg,whereby liquid Component (B) was prepared.

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.56; the content of Constituent (B1) and Constituent (B2) was 57 vol.%, and the content of Constituent (E1) was 8.5 mass % per the sum ofConstituents (A1), (A2), and (E1). Characteristics of the obtainedthermally conductive silicone rubber composition and thermallyconductive silicone rubber were measured by the same methods as inPractical Example 1, and the results of the measurements are shown inTable 1.

Practical Example 4

A mixture was prepared by mixing for 15 min. the following components:21.39 parts by mass of Constituent (A1); 5.35 parts by mass ofConstituent (A2); 59.46 parts by mass of Constituent (B1); 106.59 partsby mass of Constituent (B2); 0.51 parts by mass of Constituent (C1);0.51 parts by mass of Constituent (C2); 4.10 parts by mass ofConstituent (E1), and 1.89 parts by mass of methyltriethoxysilane (theminimal coated surface area=439 m²/g). The obtained mixture was furthermixed for 1 hr. at 150° C. and under a reduced pressure below 10 mmHg.Following this, the contents were cooled to room temperature for 30 min.and mixed for 15 min. at room temperature with 0.22 parts by mass ofconstituent (D1) and again mixed for 30 min. at room temperature under areduced pressure below 10 mmHg. As a result, liquid Component (A) wasprepared.

Independently, another mixture was prepared by mixing for 15 min. thefollowing constituents: 17.8 parts by mass of Constituent (A1); 4.4parts by mass of Constituent (A2); 59 parts by mass of Constituent (B1);107 parts by mass of Constituent (B2): 0.50 parts by mass of Constituent(C1); 0.50 parts by mass of Constituent (C2); 4.1 parts by mass ofConstituent (E1), and 1.89 parts by mass of methyltriethoxysilane. Theobtained mixture was further mixed for 1 hr. at 150° C. and under areduced pressure below 10 mmHg. Following this, the contents were cooledto room temperature for 30 min. under mixing conditions. The obtainedmixture was further combined with 2.83 parts by mass of Constituent (D2)and 2.03 parts by mass of Constituent (F1). The contents were furthermixed at room temperature for 15 min, and then were mixed for 30 min.under a reduced pressure below 10 mmHg, whereby liquid Component (B) wasprepared.

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.56; the content of Constituent (B1) and Constituent (B2) was 55 vol.%, and the content of Constituent (E1) was 4.0 mass % per the sum ofConstituents (A1), (A2), and (E1). The content of methyltriethoxysilanewas sufficient to cover 300% of the total surface area of bothConstituents (B1) and (B2). Characteristics of the obtained thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured by the same methods as in Practical Example 1, andthe results of the measurements are shown in Table 1.

Practical Example 5

A mixture was prepared by mixing for 15 min. the following components:153.18 parts by mass of Constituent (A1); 38.25 parts by mass ofConstituent (A2); 750.30 parts by mass of Constituent (B1); 509.70 partsby mass of Constituent (B2); 3.75 parts by mass of Constituent (C1);3.75 parts by mass of Constituent (C2); 30.00 parts by mass ofConstituent (E1), and 9.54 parts by mass of methyltriethoxysilane (theminimal coated surface area=439 m²/g). The obtained mixture was furthermixed for 1 hr. at 150° C. and under a reduced pressure below 10 mmHg.Following this, the contents were cooled to room temperature for 1 hr.and mixed for 15 min. at room temperature with 1.53 parts by mass ofconstituent (D1) and again mixed for 30 min. at room temperature under areduced pressure below 10 mmHg. As a result, liquid Component (A) wasprepared.

Independently, another mixture was prepared by mixing for 15 min. thefollowing constituents: 124.00 parts by mass of Constituent (A1); 32.40parts by mass of Constituent (A2); 750.30 parts by mass of Constituent(B1); 509.70 parts by mass of Constituent (B2); 3.75 parts by mass ofConstituent (C1); 3.75 parts by mass of Constituent (C2); 30.00 parts bymass of Constituent (E1), 1.20 parts by mass of Constituent (G1), and9.54 parts by mass of methyltriethoxysilane. The obtained mixture wasfurther mixed for 1 hr. at 150° C. and under a reduced pressure below 10mmHg. Following this, the contents were cooled to room temperature for 1hr. under mixing conditions. The obtained mixture was further combinedwith 20.40 parts by mass of Constituent (D2) and 15.00 parts by mass ofConstituent (F1). The contents were further mixed at room temperaturefor 30 min, and then were mixed for 30 min. under a reduced pressurebelow 10 mmHg, whereby liquid Component (B) was prepared.

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.52; the content of Constituent (B1) and Constituent (B2) was 57 vol.%, and the content of Constituent (E1) was 4.1 mass % per the sum ofConstituents (A1), (A2), and (E1). The content of methyltriethoxysilanewas sufficient to cover 278% of the total surface area of bothConstituents (B1) and (B2). Characteristics of the obtained thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured by the same methods as in Practical Example 1, andthe results of the measurements are shown in Table 1.

Practical Example 6

A mixture was prepared by mixing for 15 min. the following components:168.00 parts by mass of Constituent (A3); 42.62 parts by mass ofConstituent (A4); 741.00 parts by mass of Constituent (B1); 504.00 partsby mass of Constituent (B2); 3.78 parts by mass of Constituent (C1);3.77 parts by mass of Constituent (C2); 33.30 parts by mass ofConstituent (E1), and 2.40 parts by mass of methyltrimethoxysilane (theminimal coated surface area=575 m²/g). The obtained mixture was furthermixed for 1 hr. at 150° C. and under a reduced pressure below 10 mmHg.Following this, the contents were cooled to room temperature for 1 hr.and mixed for 15 min. at room temperature with 1.60 parts by mass ofconstituent (D1) and again mixed for 30 min. at room temperature under areduced pressure below 10 mmHg. As a result, liquid Component (A) wasprepared.

Independently, another mixture was prepared by mixing for 15 min. thefollowing constituents: 138.40 parts by mass of Constituent (A3); 36.50parts by mass of Constituent (A4); 742.00 parts by mass of Constituent(B1); 504.00 parts by mass of Constituent (B2); 3.77 parts by mass ofConstituent (C1); 3.79 parts by mass of Constituent (C2); 33.50 parts bymass of Constituent (E1), 1.20 parts by mass of Constituent (G1), and2.30 parts by mass of methyltrimethoxysilane. The obtained mixture wasfurther mixed For 1 hr. at 150° C. and under a reduced pressure below 10mmHg. Following this, the contents were cooled to room temperature for 1hr. under mixing conditions. The obtained mixture was further combinedwith 21.62 parts by mass of Constituent (D2) and 15.00 parts by mass ofConstituent (F1). The contents were further mixed at room temperaturefor 30 min, and then were mixed for 30 min. under reduced pressure below10 mmHg. As a result, liquid Component (B) was prepared.

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A3) and (A4) was1.53; the content of Constituent (B1) and Constituent (B2) was 55 vol.%, and the content of Constituent (E1) was 4.1 mass % per the sum ofConstituents (A3), (A4), and (E1). The content of methyltriethoxysilanewas sufficient to cover 90.6% of the total surface area of bothConstituents (B1) and (B2). Characteristics of the obtained thermallyconductive silicone rubber composition and thermally conductive siliconerubber were measured by the same methods as in Practical Example 1, andthe results of the measurements are shown in Table 1.

Comparative Example 1

Liquid Component (A) was prepared by mixing at room temperature thefollowing components: 6.30 parts by mass of Constituent (A1); 1.40 partsby mass of Constituent (A2); 25.01 parts by mass of Constituent (B1);16.99 parts by mass of Constituent (B2); 0.13 parts by mass ofConstituent (C1); 0.13 parts by mass of Constituent (C2); and 0.05 partsby mass of Constituent (D1).

Independently, liquid Component (B) was prepared by mixing at roomtemperature the following constituents: 5.43 parts by mass ofConstituent (A1); 1.20 parts by mass of Constituent (A2); 25.01 parts bymass of Constituent (B1); 16.99 parts by mass of Constituent (B2); 0.13parts by mass of Constituent (C1); 0.13 parts by mass of Constituent(C2); 0.61 parts by mass of Constituent (D2); and 0.50 parts by mass ofConstituent (F1).

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.54; the content of Constituent (B1) and Constituent (B2) was 57 vol.%. Characteristics of the obtained thermally conductive silicone rubbercomposition and thermally conductive silicone rubber were measured bythe same methods as in Practical Example 1, and the results of themeasurements are shown in Table 1.

Comparative Example 2

Liquid Component (A) was prepared by mixing at room temperature thefollowing components: 25.36 parts by mass of Constituent (A1); 5.43parts by mass of Constituent (A2); 100.00 parts by mass of Constituent(B1); 68.00 parts by mass of Constituent (B2); 0.50 parts by mass ofConstituent (C1); and 0.49 parts by mass of Constituent (C2). Thecontents were mixed for 1 hr. at 150° C. under a reduced pressure below10 mmHg and then were cooled for 30 min. to room temperature. Followingthis, 0.22 parts by mass of Constituent (D1) were added, mixing wascarried out at room temperature first for 15 min. and then for 30 min.under a reduced pressure below 10 mmHg. As a result, liquid Component(A) was prepared.

Independently, liquid Component (B) was prepared by mixing at roomtemperature the following constituents: 20.55 parts by mass ofConstituent (A1); 4.40 parts by mass of Constituent (A2); 100.00 partsby mass of Constituent (B1); 68.00 parts by mass of Constituent (B2);0.50 parts by mass of Constituent (C1); 0.50 parts by mass ofConstituent (C2); and 1.60 parts by mass of fumed silica havingBET-specific surface area of 200 m²/g. The contents were mixed for 1 hr.at 150° C. under a reduced pressure below 10 mmHg and then were cooledfor 30 min. to room temperature. Following this, 2.45 parts by mass ofConstituent (D2) and 2.0 parts by mass of Constituent (F1) were added,and mixing was carried out at room temperature for 30 min. under areduced pressure below 10 mmHg. As a result, liquid Component (B) wasprepared.

A thermally conductive silicone rubber composition was prepared bymixing the aforementioned liquid Components (A) and (B) in a 1:1 ratio.In the prepared thermally conductive rubber composition, the mole ratioof silicon-bonded hydrogen atoms contained in Constituent (D2) to thetotal amount of vinyl groups contained in Constituents (A1) and (A2) was1.56; the content of Constituent (B1) and Constituent (B2) was 57 vol.%. Characteristics of the obtained thermally conductive silicone rubbercomposition and thermally conductive silicone rubber were measured bythe same methods as in Practical Example 1, and the results of themeasurements are shown in Table 1.

TABLE 1 Example No. Practical Examples Comparative ExamplesCharacteristics 1 2 3 4 5 6 1 2 Viscosity (Pa · s) 0.3 rpm 114.8 107.5133.9 156.1 122.7 68.4 109.0 517 3.4 rpm 72.0 57.0 77.3 102.3 78.0 55.757.1 51.6 Coefficient of Thermal 1.586 1.416 1.537 1.275 1.547 1.4751.585 1.447 Conductivity (W/m · K) Adhesive Strength (N/cm²) 303 389 383401 318 344 213 284 Elongation (%) 80.0 67.5 68.0 77.0 75.0 76.3 65.073.0 Tensile Strength (MPa) 6.09 6.94 7.53 6.00 5.64 5.84 4.06 5.69Hardness 90 92 93 88 92 88 83 90

INDUSTRIAL APPLICABILITY

Since the thermally conductive silicone rubber composition of theinvention is characterized by good flowability and handleability priorto curing and since, when cured, it is turned into a thermallyconductive silicone rubber that possesses good adhesive properties,elongation characteristics and tensile strength, it is suitable for useas a heat-removing adhesive and sealant for units and parts ofelectrical and electronic devices.

1. A thermally conductive silicone rubber composition comprising: (A) anorganopolysiloxane with the exception of below-given components (C) and(E); (B) a thermally conductive filler; (C) a composition selected from(i) an organopolysiloxane represented by the following general formula:[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d) (wherein R¹ is a univalent hydrocarbon group withan aliphatic, unsaturated bonds, R² may designate the same or differentunivalent hydrocarbon groups that do not have aliphatic, unsaturatedbonds, R³ designates an alkyl group, alkoxyalkyl group, alkenyl group,or an acyl group; “a” is an integer between 0 and 3, “b” is 1 or 2, “c”is an integer between 1 and 3, “d” is an integer between 1 and 3;“(c+d)” is an integer between 2 and 4, “m” is an integer that is equalto or greater than 0, and “n” is an integer that is equal to or greaterthan 0; when “a” is 0, then “m” is an integer that is equal to orgreater than 1); (ii) an organopolysiloxane represented by the followinggeneral formula:R⁴ ₃SiO(R⁴ ₂SiO)_(p)R⁴ ₂Si—R⁵—SiR⁴ _((3−d))(OR³)_(d) (wherein R³ is thesame defined above, R⁴ represents the same or different univalenthydrocarbon groups, R⁵ represents an oxygen atom or a bivalenthydrocarbon group, “p” is an integer between 100 and 500, and “d” is thesame defined above); or (iii) a mixture of two or more of the aboveconstituents (i) and (ii); (D) a curing agent; and (E) anorganopolysiloxane composed of the following units: SiO_(4/2), R¹R²₂SiO_(1/2), and R² ₃SiO_(1/2) (wherein R¹ and R² are the same as definedabove), with the proviso that component (E) is used in an amount of 2 to10 mass % per sum of components (A) and (E).
 2. The thermally conductivesilicone rubber composition of claim 1, wherein said Component (B) hasan average particle size within the range of 0.1 to 100 μm.
 3. Thethermally conductive silicone rubber composition of claim 1, whereinsaid Component (B) is an alumina powder.
 4. The thermally conductivesilicone rubber composition of claim 3, wherein the BET specific surfacearea of said Component (B) is equal to or below 5.0 m²/g.
 5. Thethermally conductive silicone rubber composition of claim 3, whereinsaid Component (B) comprises a mixture of spherical alumina powder (B₁)with an average particle size in the range of 1 to 30 μm (excluding 1 μmparticles) and a spherical or irregular-shaped alumina powder (B₂) withan average particle size in the range of 0.1 to 5 μm.
 6. The thermallyconductive silicone rubber composition of claim 5, wherein saidComponent (B) comprises 30 to 90 mass % of said constituent (B₁) and 10to 70 mass % of said constituent (B₂).
 7. The thermally conductivesilicone rubber composition of claim 1, wherein said Component (B) isused in an amount of 300 to 2,500 parts by mass per 100 parts by mass ofsaid Component (A).
 8. The thermally conductive silicone rubbercomposition of claim 1, wherein said Component (C) is used in an amountof 0.1 to 10 parts by mass per 100 parts by mass of said Component (B).9. The thermally conductive silicone rubber composition of claim 1,wherein said Component (B) is surface-treated with said Component (C) insaid Component (A).
 10. The thermally conductive silicone rubbercomposition of claim 1, wherein said thermally conductive siliconerubber composition is cured in a hydrosilylation reaction, condensationreaction, or by a free-radical reaction with the use of an organicperoxide.
 11. A thermally conductive silicone rubber compositioncomprising: (A) an organopolysiloxane with the exception of below-givencomponents (C) and (E); (B) an alumina powder as a thermally conductivefiller having an average particle size within the range of 0.1 to 100μm; (C) a composition selected from (i) an organopolysiloxanerepresented by the following general formula:[R¹ _(a)R² _((3−a))SiO(R¹ _(b)R² _((2−b))SiO)_(m)(R² ₂SiO)_(n)]_(c)SiR²_([4−(c+d)])(OR³)_(d) (wherein R¹ is a univalent hydrocarbon group withan aliphatic, unsaturated bonds, R² may designate the same or differentunivalent hydrocarbon groups that do not have aliphatic, unsaturatedbonds, R³ designates an alkyl group, alkoxyalkyl group, alkenyl group,or an acyl group; “a” is an integer between 0 and 3, “b” is 1 or 2, “c”is an integer between 1 and 3, “d” is an integer between 1 and 3;“(c+d)” is an integer between 2 and 4, “m” is an integer that is equalto or greater than 0, and “n” is an integer that is equal to or greaterthan 0; when “a” is 0, then “m” is an integer that is equal to orgreater than 1); (ii) an organopolysiloxane represented by the followinggeneral formula:R⁴ ₃SiO(R⁴ ₂SiO)_(p)R⁴ ₂Si—R⁵—SiR⁴ _((3−d))(OR³)_(d) (wherein R³ is thesame defined above, R⁴ represents the same or different univalenthydrocarbon groups, R⁵ represents an oxygen atom or a bivalenthydrocarbon group, “p” is an integer between 100 and 500, and “d” is thesame defined above); or (iii) a mixture of two or more of the aboveconstituents (i) and (ii); (D) a curing agent; and (E) anorganopolysiloxane composed of the following units: SiO_(4/2), R¹R²₂SiO_(1/2), and R² ₃SiO_(1/2) (wherein R¹ and R² are the same as definedabove), with the proviso that component (E) is used in an amount of 2 to10 mass % per sum of components (A) and (E).
 12. The thermallyconductive silicone rubber composition of claim 11, wherein the BETspecific surface area of said Component (B) is equal to or below 5.0m²/g.
 13. The thermally conductive silicone rubber composition of claim11, wherein said Component (B) comprises a mixture of spherical aluminapowder (B₁) with an average particle size in the range of 1 to 30 μm(excluding 1 μm particles) and a spherical or irregular-shaped aluminapowder (B₂) with an average particle size in the range of 0.1 to 5 μm.